1. Field of the Invention
This invention relates to catalysts, particularly catalysts for use in fluidized bed operations. More specifically, this invention relates to the manufacture of catalysts, especially fluid catalytic cracking catalysts, and catalyst samples used in experimentation.
2. Discussion of Related Art
Fluid catalytic cracking (FCC) is a known process that cracks heavy gas oils into diesel oils and gasoline with the use of catalysts that speed up the cracking reaction. FCC uses catalysts with an ultimate particle size on the order of about 20-120 microns. The cracking process operates at temperatures of between about 450° C. and 650° C. and at contact times on the order of about 1-60 seconds. With such short contact times and high temperatures, a critical requirement for effective catalyst performance is the absence of diffusional limitations on the reaction rate. To achieve this, the size and connectivity of the pores in the catalyst must be carefully controlled.
The typical FCC catalyst is comprised of zeolites, which have an ultimate pore diameter of less than 8 Angstroms; aluminas, which have an ultimate pore diameter above 20 Angstroms; leached clays, which have an ultimate pore diameter around 45-65 Angstroms; clays, which have little porosity in their native state but which can be pillared to have ultimate pore widths of ca. 10-30 Angstroms; and, binders. The binders can include silica sols with ultimate particle sizes of around 20 Angstroms, aluminum chlorhydrol with an ultimate particle size of ca. 10 Angstroms, and peptized alumina with an ultimate particle size of ca. 30 Angstroms. The binders can create porosity by the manner in which they bind together the larger components in the slurry upon drying. For example if the binder sols react first with each other and then with the larger components, they tend to “gel.” Gels are intrinsically viscous, and require significant dilution before their viscosity is low enough to allow spray drying. Control of the pore size distributions in gels is poorer than in sol systems.
One method of choice for preparing large quantities of microspheroids of the particle size that can be used as catalysts in FCC is spray drying. However, spray drying is not the choice for the preparation of small quantities of catalysts, especially small quantities of catalysts suitable for application in high throughput experimentation (HTE). HTE is a useful tool for increasing the rate of experimentation and improving and accelerating the possibility of making discoveries of new products and processes. It would be beneficial to use HTE techniques to experiment on process variables and the composition of catalysts used in refining operations, particularly in FCC.
The amount of material suitable for HTE (about 50 g), if run in a scaled down spray drier, would either stick to the walls or have ultimate particle sizes that are too low because the drying time (free fall time in the spray drier) would be too short. Since slow diffusion of gas oil molecules can limit the extent of their reaction, it is critical that any catalyst made for HTE has the same ultimate particle size as a commercially prepared catalyst. It is also critical that the drying procedure (e.g., slurry density, viscosity, and time-temperature-gas composition distribution in the drier) has the potential to recreate the controlling variables for the pore size distribution in the spray drier operation.
Thus, there is a need for a method of manufacturing small quantities of controlled particle size catalysts, particularly catalysts used in fluidized bed operations such as FCC, for high throughput experimentation and a device for practicing the method. There is also a need for manufacturing small quantities of particles having a size and pore distribution that is equivalent to commercially produced particles.